Space
How much mass does the Sun lose every second?
Every second, the Sun converts about 4 million tonnes of its own mass into energy through nuclear fusion.
Source: Solar luminosity 3.8 × 10²⁶ W, via E = mc².
Context
About 4 million tonnes. The Sun's output is 3.8 × 10²⁶ watts, and dividing that by the speed of light squared, as in E = mc², gives the mass converted into energy each second.
The mass is lost in fusing hydrogen into helium, not burned away like fuel. The Sun has enough hydrogen that this loss is a rounding error on its total mass.
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